•Classification of cavitation as stable or inertial is inadequate in some cases.•Cavitation intensity may be underestimated due to inaccurate frequency filtering.•Pure cavitation noise should be used ...to character cavitation intensity.
Cavitation intensity is used to describe the activity of cavitation, and several methods are developed to identify the intensity of cavitation. This work aimed to provide an overview and discussion of the several existing characterization methods for cavitation intensity, three acoustic approaches for charactering cavitation were discussed in detail. It was showed that cavitation noise spectrum is too complex and there are some differences and disputes on the characterization of cavitation intensity by cavitation noise. In this review, we recommended a total cavitation noise intensity estimated via the integration of real cavitation noise spectrum over full frequency domain instead of artificially adding inaccurate filtering processing.
A study on the transient behavior of a single-loop optoelectronic oscillator (OEO) under a single sinusoidal radio frequency (RF) signal injection is presented. Considering only the phase ...perturbation imposed by the external RF signal, the phase-dynamic equation is solved to analyze the frequency settling behavior of the loop. A closed form expression for the required time of an OEO under RF injection-locking, reaching the steady state condition, is derived in terms of the initial phase difference, beat frequency and injection signal strength. The phase modulated signal, which is responsible for the perturbation of the free running oscillation, is expanded in a Fourier series and the expression for the output RF spectrum of the injection pulled OEO is derived. The injection-pulling dynamics approach is used to describe the phase noise of the OEO and also, the influence of the phase settling time constant on the phase noise of the injection-locked OEO is studied. The experimental results corroborating the theoretical findings are given.
Underwater acoustic target recognition based on ship radiated noise has always been a challenging task due to the complexity of underwater environment and the antagonism of targets. An underwater ...acoustic target recognition network based on Ship radiated Noise spectrum component Analysis (SNANet) is proposed in this paper by extracting the spectrum features of each component in different frequency bands, which improves the recognition accuracy as compared with existing end-to-end recognition methods. Adaptive weight based on forward weight and backward weight is used to fuse main and auxiliary features. Experiments have demonstrated that SNANet surpasses currently existing models in performance on the public dataset DeepShip.
•SNANet employs Ship radiated Noise spectrum component Analysis to utilize frequency bands of each component.•The main and auxiliary features are fused with adaptive weights to obtain a robust feature.•SNANet demonstrates superior recognition performance on DeepShip compared to end-to-end methods.
Dense ensembles of spin qubits are valuable for quantum applications, even though their coherence protection remains challenging. Continuous dynamical decoupling can protect ensemble qubits from ...noise while allowing gate operations, but it is hindered by the additional noise introduced by the driving. Concatenated continuous driving (CCD) techniques can, in principle, mitigate this problem. Here we provide deeper insights into the dynamics under CCD, based on Floquet theory, that lead to optimized state protection by adjusting driving parameters in the CCD scheme to induce mode evolution control. We experimentally demonstrate the improved control by simultaneously addressing a dense nitrogen-vacancy (NV) ensemble with 1010 spins. We achieve an experimental 15-fold improvement in coherence time for an arbitrary, unknown state, and a 500-fold improvement for an arbitrary, known state, corresponding to driving the sidebands and the center band of the resulting Mollow triplet, respectively. We can achieve such coherence time gains by optimizing the driving parameters to take into account the noise affecting our system. By extending the generalized Bloch equation approach to the CCD scenario, we identify the noise sources that dominate the decay mechanisms in NV ensembles, confirm our model by experimental results, and identify the driving strengths yielding optimal coherence. Our results can be directly used to optimize qubit coherence protection under continuous driving and bath driving, and enable applications in robust pulse design and quantum sensing.
Vehicle type and driving speed are important factors affecting the vehicle noise spectrum. Therefore, according to the noise spectrum characteristics of single vehicles, the types of vehicles ...commonly found on Chinese urban roads are classified and the speed interval is divided. Then, by collecting the noise data of a large number of single vehicles, the noise spectrum characteristics of different types of vehicles at different speed intervals are analyzed. Combined with the vehicle noise emission calculation model, the sound pressure level of the vehicle is calculated, and the noise spectrum of the single vehicle is calculated by the sound pressure level and the noise spectral characteristics of the corresponding vehicle type and speed. The speed distribution of each type of vehicle is estimated, and the noise spectrum of small-size traffic flow consisting of the same type of vehicle driving at the same speed interval is calculated. Finally, the noise spectra of all small-size traffic flow on the road section are superimposed to calculate the road traffic noise spectrum. This calculation method is applied to the five cases, the range standard deviation of the spectral sound pressure level between the calculated result and the measured value is 2.24,3.14, and the range of Euclidean Distance between the spectral energy contribution rate is 0.1,0.16.
Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In ...this work, the fine-structure splitting 1s22s2S1/2−1s22p2P1/2 transition in lithium-like 16O5+ has been investigated in a laser spectroscopy experiment at the heavy-ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2S1/2−2P1/2 transition wavelength was determined to be λ0= 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high-precision divider to precisely measure the high-voltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off-axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole-forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger-scale scientific facility HIAF in China.
The optoelectronic oscillator is a delay line oscillator that leverages optical fibre technology to realize the large delay required for low phase noise systems. Spurious sidemodes are an artefact of ...the delay line oscillator, yet treatments of injection locking of optoelectronic oscillators have relied on the application of classical injection locking theory valid only for single mode oscillators. The large delay contributed by the optical fibre delay line is accounted for by the classical theory only in part through the quality factor Q that captures the round-trip group delay in a neighborhood of the oscillation frequency. This paper presents a new formulation of time delay oscillators subject to injection that describes all the essential features of their dynamics and phase noise. The common assumptions of a single mode oscillator and weak injection are removed. This is important to correctly predict the lock-in range, the suppression of sidemodes and the phase noise spectrum. The findings of the analysis are validated by experimental measurements provided by an optoelectronic oscillator under injection by an external source.
A significant deceleration effect on a stored coasting ion beam by a continuous-wave laser light was observed in the Schottky-noise spectrum during the laser experiments with lithium-like oxygen ion ...beams stored at a relativistic energy of 275.7 MeV/u at the heavy-ion storage ring CSRe in Lanzhou, China. The observed deceleration range of the laser (Δp/p≈5.7×10−6) is much broader than the expected capture range (Δp/p≈3.6×10−8), as calculated from the natural linewidth of the O5+ ion’s electronic transition (2S1/2−2P1/2). In order to explain this huge deviation, a phase space tracking code has been developed to investigate the interaction between the stored coasting ion beam and the laser light. Simulations reveal that the deceleration range of the typically narrow CW laser force is highly enlarged by taking into account the transverse betatron oscillation of the ions with larger emittance and the angular misalignment of the laser light direction. The experimental observation is well described by the systematic simulations. The present work is crucial for forthcoming laser cooling and precision laser spectroscopy experiments and simulations on heavy highly charged ions at the CSRe and the future facility HIAF.
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